1. Field of the Invention
This invention relates to hair dye preparations containing substantive hair dyes as well as some of the dyes per se. Preparations of the type in question contain substantive hair dyes in a cosmetic carrier. In many cases, such preparations additionally contain oxidation dye precursors to produce certain shades. The cosmetic carriers used for the substantive hair dyes and oxidation dye precursors, if any, are creams, emulsions, gels, shampoos, foam aerosols or other preparations suitable for application to the hair.
2. Statement of Related Art
In addition to the oxidation dyes, which are formed by the oxidative coupling of one or more developer components with one or more coupler components, substantive hair dyes play a prominent part in the dyeing of hair. Substantive dyes have the advantage of being used without the addition of oxidizing agents. The substantive dyes used are predominantly nitrobenzene derivatives. They are used either on their own or in combinations with other substantive dyes, cationic azo dyes such as anthraquinone dyes, indophenols, triphenylmethane dyes, or with oxidation dyes.
Good hair-dyeing preparations have to form the required shades with sufficient intensity. They must be readily absorbed by human hair without excessively staining the scalp. The coloring produced with them must show high stability to light, heat, perspiration, shampoos and the chemicals used in the permanent waving of hair. Finally, they should be safe to use from the toxicological and dermatological viewpoint.
Among the substantive nitrobenzene derivatives, the nitroanilines and derivatives thereof play an important part because some of these dyes produce intensive, light-stable colors. However, the known substantive nitroaniline dyes have disadvantages in that, on the one hand, they show only limited solubility in water, which leads to problems during formulation of the hair dye preparations, and on other hand they are not sufficiently fast to washing, i.e. the dye finishes fade considerably after repeated shampooing.
In addition, it is desirable that substantive dyes should be able to produce shades of red to obtain fashionable hair colors. 2-Nitro-p-phenylenediamine and amino-substituted derivatives thereof are normally used for this purpose. Unfortunately, these chemically related compounds are difficult to dissolve and difficult to disperse in water. This readily leads to uneven or to faint hair colors. Moreover, particularly where hair preparations have high concentrations of dye, the dyes crystallize out and are not adsorbed onto the hair to be dyed. Accordingly, there is an urgent need for substantive hair dyes showing improved solubility in water.
Furthermore, substantive hair dyes desirably show high compatibility with other dyes, for example with oxidation dye precursors and with the other components normally used in oxidation hair dye preparations, because substantive dyes and oxidation dyes are often combined with one another for color modification. Accordingly, high stability to reducing agents and oxidizing agents is necessary.